I'm surprised this wasn't mentioned. Chlorophyll doubles his speed. Solarbeam gets STAB and no charge time in the sun. Weather ball does the same that that hidden power fire would do, only with 100 base power, allowing it to break through steel types pretty well. HP ice and ground can both cover tons of pokemon, so pick which one concerns you the most. growth boosts up special attack more in the sun, while stockpile pads up his defenses a bit, making it a bit less prone to priority. Synthesis restores health in the sun.

Sun sweeper. Although physical is a nice touch. Swords Dance makes you do a good amount of damage along with your Life Orb. Sucker Punch is a nice touch, priority is always good to have. Power Whip can't be used along with Sucker Punch, but Leaf Blade is good enough, it replaces it with no problem. Return does nice neutral damage. I really just ran out of moves. Return isn't bad though. Your EVs are geared towards sweeping, and a tiny bit of HP for priority,

Gastro Acid and Worry Seed are used to help out Pokemon such as Archeops, Regigigas, and Slaking. However, Worry Seed doesn't work with Truant, so use Gastro Acid if you are partnering with Slaking. Otherwise use Worry Seed. Reflect offers team support. Razor Leaf is STAB that hits multiple Pokemon. It has low base power however, so Leaf Blade can be used instead. Frustration is neutral coverage.

For Double or Triple Battle: Speedy/ Powerful Victreebel
Pair with a Pokémon that knows Drought ability such as Ninetails, Charizard(holding Y megastone), or Groudon. To boost speed pair with a Pokémon that can use tailwind as priority such as Talonflame (my favorite) or Whimiscott. Also, pair with a Pokémon that knows the ability Intimidate to cut the damage of Physical flying type moves. I use Krookodile and Luxray.
EV's: Max out Sp. Attack, spread the rest on Speed(quickness) and HP(survival).
I recommend the following:
Ability: Modest or Timid
Item: Life Orb, Wise Glasses, or Focus sash
Moves: Solarbeam, Sludge Bomb, Sleep Powder, Protect